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The commit's purpose is laudable:
The only way for chardev drivers to communicate an error was to
return a NULL pointer, which resulted in an error message that
said _that_ something went wrong, but not _why_.
It attempts to achieve it by changing the interface to return 0/-errno
and update qemu_chr_open_opts() to use strerror() to display a more
helpful error message. Unfortunately, it has serious flaws:
1. Backends "socket" and "udp" return bogus error codes, because
qemu_chr_open_socket() and qemu_chr_open_udp() assume that
unix_listen_opts(), unix_connect_opts(), inet_listen_opts(),
inet_connect_opts() and inet_dgram_opts() fail with errno set
appropriately. That assumption is wrong, and the commit turns
unspecific error messages into misleading error messages. For
instance:
$ qemu-system-x86_64 -nodefaults -vnc :0 -chardev socket,id=bar,host=xxx
inet_connect: host and/or port not specified
chardev: opening backend "socket" failed: No such file or directory
ENOENT is what happens to be in my errno when the backend returns
-errno. Let's put ERANGE there just for giggles:
$ qemu-system-x86_64 -nodefaults -vnc :0 -chardev socket,id=bar,host=xxx -drive if=none,iops=99999999999999999999
inet_connect: host and/or port not specified
chardev: opening backend "socket" failed: Numerical result out of range
Worse: when errno happens to be zero, return -errno erroneously
signals success, and qemu_chr_new_from_opts() dies dereferencing
uninitialized chr. I observe this with "-serial unix:".
2. All qemu_chr_open_opts() knows about the error is an errno error
code. That's simply not enough for a decent message. For instance,
when inet_dgram() can't resolve the parameter host, which errno code
should it use? What if it can't resolve parameter localaddr?
Clue: many backends already report errors in their open methods.
Let's revert the flawed commit along with its dependencies, and fix up
the silent error paths instead.
This reverts commit 6e1db57b2ac9025c2443c665a0d9e78748637b26.
Conflicts:
console.c
hw/baum.c
qemu-char.c
This reverts commit aad04cd024f0c59f0b96f032cde2e24eb3abba6d.
The parts of commit db418a0a "Add stdio char device on windows" that
depend on the reverted change fixed up.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
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